It's easy to get comfortable in your cardiovascular workout. You walk at the same pace along the same route, or set the elliptical to the same old program. The intensity of your exercise program directly correlates to how much weight you lose, so you should exercise hard at least some of the time. However, completing 20 to 45 minutes of cardio at your maximum heart rate is not recommended for weight loss.

What Is It?

Your maximum heart rate is the absolute fastest your heart can beat per minute. It is often estimated by taking 220 minus your age, according to the American Heart Association. You can determine your max heart rate as well as your oxygen consumption with a VO2 max test, but these are done in a clinical setting with educated personnel and specialized equipment. During a VO2 max test you will gradually increase in exercise intensity until you're completely fatigued, usually within six to 10 minutes depending on the protocol. Once you hit your max most people can only maintain it for a minute or less, not 20 to 45 minutes.

Do a Fraction of the Work

The American College of Sports Medicine (ACSM) established guidelines for exercise to lose weight, and nowhere in these guidelines does it say to work at your maximum heart rate. Instead you should work at a percentage of your maximum heart rate, or a specific intensity. ACSM and the Centers for Disease Control and Prevention recommend cardio at a moderate to vigorous intensity for weight loss. This would be a range of 50 to 85 percent of your maximum heart rate. The harder you work, the more calories you will burn for weight loss.

Estimate Your Workload

You can use a basic calculation such as the Karvonen formula to estimate your max heart rate and target heart rate zones for training. Start by taking 220 and subtracting your age. This is your estimated maximum heart rate. Take your pulse for one minute after you have been sitting for a few minutes to estimate your resting heart rate. Subtract your resting heart rate from your max heart rate. This is your heart rate reserve. Multiply your heart rate reserve by 0.5 and add back in your resting heart rate. This is the low end of your work zone. Multiply your heart rate reserve by 0.85 and add in your resting heart rate to estimate the high end of your work zone. Train in this range when you perform cardio.

Check and Re-Check

As you become more fit you will need to redo your work zone calculation. Exercise at the same intensity will become easier, so increase your pace or the resistance. You need to continually reevaluate in order to lose weight and avoid a plateau. Also keep in mind how the session feels. If you have done the calculations and exercise at 85 percent, it should not feel easy. If it does it means the calculation is a bit off. Remember that these are estimates and how you feel is just as important as what your heart rate says. Vigorous exercise should be uncomfortable, but you can still say a few words. Your breathing is heavy, and you are sweating. Check how you feel as well as your heart rate.

About the Author

Bethany Kochan began writing professionally in 2010. She has worked in fitness as a group instructor, personal trainer and fitness specialist since 1998. Kochan graduated in 2000 from Southern Illinois University with a Bachelor of Science in exercise science. She is a Certified Strength and Conditioning Specialist, Certified Personal Trainer, Medical Exercise Specialist and certified YogaFit instructor.

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